Research laboratories throughout the world are currently conducting tests to study cell growth under different conditions. For example, tests are being conducted relating to control of surface topography of a cell growth surface to optimize the output of cells within a finite area. An exemplary purpose of such testing is to decrease the costs of cells used in vaccine production. For example, U.S. Pat. No. 3,976,547 to McAleer et al. discloses that a cell growth surface having irregularities increases the surface area available for cell growth. McAleer et al. obtain the irregular surface area by sintering or sputter coating metal, glass, ceramic or plastic onto a suitable substrate.
Alternatively, research is being conducted to determine how various cells interact with a wide variety of inorganic materials such as ceramics, glass, plastics and metals. The purpose of such study is as varied as the cells and inorganic materials being tested. For example, research is currently being conducted in the medical field in an attempt to locate a material that would be well suited for use in implants.
Implants are commonly inserted or grafted into the human body for either prosthetic, therapeutic, diagnostic, cosmetic or experimental purposes. Many of these implants have traditionally been made of inorganic materials that were originally developed and used for non-medical or unrelated purposes, such as aerospace applications. As a result, the inorganic materials presently available for medical implants do not necessarily have the optimal mechanical properties and inert behavior characteristics desirable for use within the body. For instance, a skeletal prostheses should be able to withstand extreme bending, buckling and torsional forces, while maintaining the ability to dampen mechanical vibrations, as well as meet stringent requirements with respect to surface hardness and abrasion resistance. In addition to the mechanical stability required, the implant should also be chemically resistant to corrosion resulting from bodily fluids and tissues, be non-toxic and meet the electro-conductivity requirements.
Because an implant is made of inorganic materials foreign to the body, it is important that the implant be biocompatible, that is, capable of coexisting with the living tissue in the surrounding human environment. At present, inorganic materials which have currently been tested and used may not be optimally suited for implants based upon their mechanical properties and inert behavior within the body. Unfortunately, relatively high costs are associated with the research and development of inorganic materials for implants.
Assessment of the interaction between cells and a wide variety of inorganic materials is an important diagnostic tool in determining the acceptability of a particular inorganic material for use in implants. Several tests including biocompatibility, cell integration, cell inductiveness, cell conductiveness, corrosiveness and toxicity may be performed to evaluate the interaction of cells with a potential implant material. To conduct the above reference tests and/or related tests the inorganic material to be tested is typically placed within a receptacle and thereby subjected to a controlled environment for interaction with cells.
At present, the desired inorganic material, for example ceramics or metals, are manufactured by conventional techniques such as casting, forging or sintering, and are then sectioned into a desired number of wafers. The wafers are mechanically ground and polished, then degreased, cleaned, passivated, sterilized and dried. Examples of this form of wafer preparation may be seen in an article by D. A. Puleo, et al. entitled Examination of Osteoblast-Orthopaedic Biomaterial Interactions Using Molecular Techniques appearing in Biomaterials, Vol. 14, No. 2, pp. 111-114 (1993) and in an article written by W. C. A. Vrouwenvelder, et al. entitled Histological and Biochemical Evaluation of Osteoblast Cultured on Bioactive Glass, Hydroxyapatite, Titanium Alloy and Stainless Steel appearing in Journal of Biomedical Materials Research, Vol. 27, pp. 465-475 (1993). The problem with using wafers for testing the interaction of cells with each of the respective inorganic materials is the cost associated with producing or purchasing such wafers, the delicacy in which they must be handled, as well as the associated time and effort involved preparing the wafers for use.
The interaction of cells with the various implant materials is determined based upon a number of factors. One such factor is the degree of roughness of the surface of the material. If the surface topography is rough, the cells rely on mechanical interlocking or interdigitation to attach to the growth surface. Mechanical interlocking is schematically illustrated by the greatly enlarged portion of a prior art cell culture apparatus 5 shown in FIG. 1. The cell culture apparatus 5 includes a metal layer 6 on a substrate 7, and wherein the cell growth surface 8 of the metal layer has pockets or indentations of a size equal to or larger than the size of a cell 8. Accordingly, the entire cell 9 or an extension thereof fits within and attaches to the pocket defined on the growth surface via mechanical interlocking.
To date, testing done relating to cell growth has focused primarily on mechanical interlocking of the cell with the growth surface. Or more to the point, current research has tested factors effecting cell growth in reliance on mechanical interlocking. Along these lines, U.S. Pat. No. 5,018,847 to Ojima et al., for example, discloses an instrument for cultivation and observation of cells using a transparent biocompatible ceramic coating. The growth surface is preferably formed by flame spray coating or plasma spray coating which are typically used to produce a relatively rough surface, although Ojima et al. fails to suggest surface roughness as being of interest. Along these lines, U.S. Pat. No. 3,939,834 to McMahon discloses a container which is coated on the interior surface with a coherent barrier layer of metal formed by sputtering to thereby form an impermeable barrier between the receptacle interior walls and the receptacle contents.